The present invention relates to a substrate for an organic electroluminescence display element, which is a light emission type display for a domestic television receiver and a terminal display device for a high information processing, a method of manufacturing the same, and an organic electroluminescence display element.
In the following description, the xe2x80x9celectro-luminescencexe2x80x9d element is often referred to as xe2x80x9cELxe2x80x9d element.
An organic EL display element, which is one of flat panel type display devices, is constructed basically such that an organic EL medium layer is sandwiched between a first electrode (anode or cathode) and a second electrode (cathode or anode). Light is emitted by allowing an electric current to flow between the two electrodes. The organic EL display element is of a self-light emission type and, thus, exhibits a high brightness and a wide viewing angle. In addition, the display element can be driven under a low voltage. In general, each of the first and second electrodes consists of a plurality of electrode lines that are arranged such that the first electrode lines and the second electrode lines cross each other to form a matrix structure. That portion of the organic EL medium layer which is positioned at the intersection between the first electrode line and the second electrode line constitutes a pixel.
In order to manufacture a large capacity and high precision organic EL display element having a matrix electrode structure, a very fine patterning treatment must be applied to the electrode line.
In general, a photolithography method or a masked vapor deposition method is known as a method for forming a fine pattern of a thin film.
However, if the second electrode layer is patterned by the photolithography method, the solvent of the photoresist or the developing solution permeates into the underlying layer of the organic EL medium layer so as to bring about rupture or deterioration of the element.
On the other hand, in the case of the masked vapor deposition method, it is important to pay attentions to the bonding strength between the vapor deposition mask and the substrate. If the bonding strength is unsatisfactory, the evaporated material is partly deposited on the back side of the vapor deposition mask pattern so as to lower the resolution. If the vapor deposition mask is forcedly bonded to the substrate in an attempt to avoid the difficulty noted above, the organic EL medium layer itself is scratched.
A method for finely patterning the second electrode line without imparting damage to the organic EL medium layer is disclosed in Japanese Patent Disclosure (Kokai) No. 5-258859 and Japanese Patent Disclosure No. 5-258860. Specifically, disclosed is a technology of oblique vapor deposition of an organic EL medium and a metal using a plurality of partition walls. In this method, a plurality of partition walls are formed to cross the anode pattern, followed by obliquely applying vapor deposition for forming the organic EL medium layer and the cathode in the order mentioned. In this method, lamination and patterning of the organic EL medium and the cathode material are carried out simultaneously. In this method, however, it is difficult to carry out the vapor deposition while rotating the substrate and to control uniformly the directions of the vapor deposition beams over a large area. In addition, the anode pattern is limited to a linear pattern.
An improvement of the partition wall oblique or slant vapor deposition method outlined above is disclosed in Japanese Patent Disclosure No. 8-315981 and Japanese Patent Disclosure No. 9-102393. In the method disclosed in these prior arts, used is a partition wall having an overhanging structure (inversely tapered partition wall or a partition wall having a T-shaped cross section). The particular partition wall is mounted to the substrate having a first electrode line formed thereon. These conventional partition wall methods make it possible in principle to carry out the vapor deposition and patterning of the organic EL medium and the second electrode line simultaneously by utilizing the presence of the partition wall. It should be noted that, since the partition wall has an overhanging structure, the patterning can be performed by the vapor deposition in a direction perpendicular to the substrate, with the result that the vapor deposition can be performed while rotating the substrate.
However, in the case of using an inversely tapered partition wall, it is possible for the incident angle of the vapor deposition beam to be smaller than the tapered angle. In this case, deposition takes place also on the side wall of the partition wall, leading to possibility of short-circuiting between the two electrodes. It follows that the method using an inversely tapered partition wall is not adapted for the vapor deposition on a substrate having a large area. On the other hand, complex steps are required for forming a partition wall having a T-shaped cross section. Further, since there is a clearance between the partition wall and the organic EL medium layer, a difficulty is brought about if vapor deposition of the organic EL medium and the second electrode material are carried out by using the partition wall. Specifically, the second electrode material is also deposited on the region where the organic EL medium layer is not present. As a result, the second electrode is brought into direct contact with the first electrode, leading to short-circuiting that impairs the normal operation of the device. Even if the second electrode material is selectively deposited on the organic EL medium so as to prevent the short-circuiting, electric field is concentrated in the vicinity of the end portion of the second electrode in which the organic EL medium is laminated thin or in the edge portion of the second electrode line so as to bring about deterioration caused by insulation breakdown or Joule heat. For preventing these problems, it is proposed to form an electric insulating layer in the base portion of the partition wall. However, formation of the insulating layer makes the manufacturing process complex. Further, since the edge portion of the organic EL medium layer/second electrode line is exposed to the outside, deterioration tends to take place from the edge portion. In addition, since a clearance is provided between the partition wall and the organic EL medium layer/second electrode line, or since light is transmitted through the partition wall, the light coming from the back surface of the substrate runs through the clearance or the partition wall to reach the display surface so as to inhibit the display.
A second problem relating to the organic EL display element is that the resistance of the anode line is increased as the anode line is made finer. If the resistance of the anode line is increased, the voltage drop caused by the resistance of the anode line is increased in the case where a current required for obtaining a sufficient brightness is allowed to flow through the anode line. As a result, a high driving voltage is required. Even in the voltage driving type device such as a liquid crystal display device or an AC type inorganic EL display element, it is necessary to decrease the resistance of the electrode line including a transparent conductor film in order to make the display characteristics uniform over the entire display panel. When it comes to a current driving type element such as a organic EL display element, it is more necessary to decrease the resistance.
Various techniques for decreasing the resistance of the anode line are disclosed in, for example, Japanese Patent Disclosure No. 10-106751 and Japanese Patent Disclosure No. 9-230318. Specifically, Japanese Patent Disclosure No. 10-106751 teaches that conductive metal lines are formed in contact with both side surfaces of a transparent electrode line so as to decrease the resistance of the anode line. In this case, however, the height of the conductive metal line is limited by the height of the transparent electrode line, making it difficult to further decrease the resistance of the anode line, though the resistance can be lowered to some extent.
On the other hand, Japanese Patent Disclosure No. 9-230318 teaches that the clearance between adjacent metal wirings is filled with an ultraviolet (UV) curing resin for the flattening purpose. However, since patterning of a transparent electrode is required in this method, the manufacturing process is rendered complex. Also, what should be particularly pointed out in this case is that, when the transparent electrode material is patterned with an etchant, the metal wiring is unavoidably corroded by the etchant. It is certainly possible to prevent the metal wiring from being corroded by allowing the side edge of the transparent electrode line to extend over the metal wiring so as to cover the adjacent UV curing resin. However, if a color display is to be obtained by the particular construction, it is impossible to obtain display of pure colors because colors are mixed.
A third problem relating to the organic EL display element is that the organic EL medium layer and the second electrode line are deteriorated.
Specifically, the organic EL medium layer and the second electrode line are deteriorated by the water, oxygen, etc. contained in the atmosphere. In order to prevent the second electrode and the organic EL medium from being deteriorated by the water, oxygen, etc., the second electrode line and the organic EL medium are sealed by a cover covering the second electrode line and the organic EL medium. For example, a box-shaped cover covering the second electrode line and the organic EL medium is bonded to the substrate under vacuum or under an inert gas atmosphere so as to hermetically seal the second electrode line and the organic EL medium.
However, some problems are brought about in the case of using a cover. First of all, when the box-shaped cover is mounted to the substrate, it is possible for the bottom surface of the cover wall to be brought into direct contact with the second electrode line so as to cause short-circuiting. It is also possible for the second electrode or the organic EL medium layer to be scratched by the bottom surface of the cover wall so as to cause short-circuiting or a poor light emission.
It should also be noted that the bottom surface of the cover wall facing the front surface of the substrate is coated with an adhesive for bonding the box-shaped cover to the substrate. Since the adhesive exhibits a fluidity, the adhesive layer is partly moved so as to contact the organic EL medium layer or the second electrode line. As a result, the organic EL medium layer or the second electrode line is deteriorated.
An object of the present invention is, therefore, to overcome at least one of the above-noted problems inherent in the conventional techniques.
To be more specific, a first object of the present invention is to provide a substrate for an organic EL display element having an improved partition wall structure that can be manufactured without making the structure complex and without imposing a big limitation to the manufacturing process, a method of manufacturing the same, and an organic EL display element.
A second object of the present invention is to provide a substrate for an organic EL display element that permits lowering the electric resistance of the anode line in an organic EL display element having a large display screen of a high fineness, an organic EL display element, and a method of manufacturing the same.
Further, a third object of the present invention is to provide a substrate for an organic EL display element that permits preventing the second electrode line and the organic EL medium layer from being damaged and deteriorated and also permits sealing easily these second electrode line and the organic EL medium layer and an organic EL display element.
The first object of the present invention is achieved according to a first aspect of the present invention by a substrate for an organic EL display element, comprising, on a support, a plurality of first electrode lines arranged apart from each other, and a plurality of partition walls arranged apart from each other and extending in a direction to cross the first electrode lines, each of the partition walls having eaves in an upper portion and flared side surfaces in a lower portion.
The substrate according to the first aspect of the present invention can be manufactured by coating a support having a plurality of first electrode lines formed thereon with a negative photoresist layer; for the negative photoresist layer, applying light exposure to expose a plurality of regions corresponding to top portions including eaves of the partition walls to light; and subsequently developing the non-exposed portion. After the development, it is desirable to perform post-baking in the present invention after irradiation with an electron beam or a UV light.
Alternatively, the substrate according to the first aspect of the present invention can be manufactured preferably by forming a negative photoresist layer on a support having first electrode lines formed thereon; for the negative photoresist layer, applying, simultaneously or one before the other, a first light exposure to expose a plurality of first regions corresponding to top portions including eaves of partition walls to light, and a second light exposure to expose a plurality of second regions corresponding to at least the flared lower end portions of the partition walls to light; and developing the non-exposed portion to form the partition walls.
Alternatively, the substrate according to the first aspect of the present invention can be manufactured preferably by forming a negative photoresist layer on a support having first electrode lines formed thereon; for the negative photoresist layer, applying, simultaneously or one before the other, a first light exposure to expose a plurality of regions corresponding to top portions including eaves of partition walls to light, and a second light exposure to expose regions corresponding to the bottoms of the partition walls to light; and developing the nonexposed portion to form the partition walls.
Further, the substrate according to the first aspect of the present invention can be manufactured preferably by forming a negative photoresist layer on a support having first electrode lines formed thereon; and, for the negative photoresist layer, applying a first light exposure to expose a plurality of first regions corresponding to top portions including eaves of partition walls to light, developing the non-exposed portion in a predetermined thickness, then applying a second light exposure to expose a plurality of second regions corresponding to the flared lower end portions of the partition walls to light, and developing the non-exposed portion to form the partition walls.
In the substrate for an organic EL display element in a preferred embodiment according to the first aspect of the present invention, the adjacent partition walls are connected to each other at the flared lower end portions by a plurality of connection bands.
The particular substrate of the preferred embodiment can be manufactured by exposing also a region connecting adjacent partition walls to light in the second light exposure step included in the method of manufacturing a substrate for an organic EL display element according to the first aspect.
The substrate for an organic EL display element in a preferred embodiment of the first aspect can also be manufactured by utilizing a plurality of color filters arranged on a support. To be more specific, the particular substrate can be manufactured by arranging a plurality of color filters apart from each other on a support to form rows and columns of the color filters; forming a plurality of first electrode lines apart from each other on the color filters in a manner to extend in the row direction of the color filters; forming a negative photoresist layer on the first electrode lines; for the negative photoresist layer, applying, simultaneously or one before the other, a first light exposure to first regions corresponding to the top portions including eaves of the partition walls, and a second light exposure, with the color filters used as a mask, to second regions corresponding to the bottom portions of the partition walls positioned between adjacent columns of the color filters and third regions positioned between adjacent rows of the color filters, from rear side of the support; and developing the non-exposed portion to form partition walls connected to each other by a connection band corresponding to the third region.
The second object of the present invention is achieved according to a second aspect of the present invention by a substrate for an organic electroluminescence display element, comprising, on a support, a plurality of first electrode lines arranged apart from each other on the support, and a plurality of conductive bus lines extending substantially in parallel to the first electrode lines, the first electrode lines being arranged apart from the support and one side edge portion of the first electrode line extending over the surface of the adjacent conductive bus line.
The substrate for an organic EL display element according to the second aspect of the present invention can be manufactured by forming a plurality of electrically insulating layers that are inversely tapered on a support; forming an electrically conductive material layer on substantially the entire surface of the support having the insulating layers formed thereon; forming a plurality of electrically conductive bus lines each connected to only one side edge of each of the insulating layers by removing that portion of the conductive material layer which is positioned on the insulating layer such that the conductive material layer remaining on the surface of the support is in contact with the one side edge of the insulating layer and is separated from the other side edge of the insulating layer; and forming a plurality of first electrode lines by forming a first electrode layer on the support having the insulating layers and the conductive bus lines formed thereon, each of the first electrode lines being positioned on the insulating layer and extending over the conductive bus line connected to the insulating layer, and the plural first electrode layers being separated from each other at the other edges of the insulating layers.
The third object of the present invention is achieved according to a third aspect of the present invention by a substrate for an organic EL display element, comprising, on a support, a plurality of first electrode lines arranged apart from each other on the support, a plurality of partition walls arranged apart from each other and extending in a direction to cross the first electrode lines, and a frame on which a cover is disposed, the frame being arranged to surround the plural partition walls.
The present invention also provides an organic electroluminescence display element comprising a substrate for an organic EL display element according to the present invention, and an organic EL medium and second electrode lines, formed on the substrate.
Further developments of the present invention are defined in the appended claims.